Semester

Fall

Date of Graduation

2004

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Wood Science and Technology

Committee Chair

Ray R. Hicks, Jr.

Abstract

This study consists of two parts, provides data on the interference between Ziziphus spina-christi, native to Saudi Arabia, and Prosopis juliflora, an introduced species. Dry leaves from both species were milled and used to prepare extracts using 0g/l, 5g/l, 20g/l, 40g/l, 60g/l, and 100 g/l of dried leaves. Leaf extract of P. juliflora was used to irrigate Z. spina-christi with 120 ml weekly over a 7-month growth period, and vice versa. Plant height, plant diameter, number of leaves, leaf area, chlorophyll content, total root length, number of root tips, root diameter, root surface area, root volume, shoot dry weight, root dry weight, and root to shoot ratio were measured monthly. Ziziphus spinachristi leaf extract produced a negative impact on all studied parameters of P. juliflora and the negative impact increased with increasing extract concentrations. Lower leaf concentration extracts of P. juliflora positively affected the studied parameters of Z. spina-christi. At 60 g/l the growth of Z. spina-christi was highly stimulated but at 100 g/l all the growth parameters were reduced. The study explored the negative effect of Z. spina-christi leaf extracts on the growth of other plant species where no such study has been conducted before.;The second part is a study of the effect of interaction between interspesific competition and nitrogen levels on growth of Prosopis juliflora and Ziziphus spina-christi seedlings for 7-months. Dry weight, root:shoot ratio, leaf area, plant height, plant diameter, total chlorophyll, relative yield, and aggressivity were measured and/or calculated. In mixed plantings with a high level of nitrogen, Prosopis juliflora exceeded the growth of the native species in most studied parameters but the effect of intraspesific competition was high. Under a low level of nitrogen the native species growth exceeded that of P. juliflora. In monoculture plantings, both species showed a reduction in growth parameters with increasing numbers of plants per pot and the reduction in low levels of nitrogen exceeded that in high levels of nitrogen. For total dry weight and leaf area, seedlings of Z. spina-christi grown in low levels of nitrogen exceeded that of seedlings grown in high levels of nitrogen.

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